DIGITALNA ARHIVA ŠUMARSKOG LISTA
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ŠUMARSKI LIST 1-2/1972 str. 44 <-- 44 --> PDF |
UDK 634.0.453:634.0.562.2:634.0.174.7 Abies alba ISTRAŽIVANJA O UTJECAJU DEFOLIJATORA NA PRIRAST JELOVIH ŠUMA Prof. dr DUŠAN KLEPAC Zavod za istraživanja u šumarstvu Šumarskog fakulteta u Zagrebu UVOD U okviru kompleksnih istraživanja o »Epidemijskom ugibanju i sušenju obične jele (Abies alba Mili), moja se uloga sastojala u tome, da između ostaloga istražim, kakve posljedice ima spomenuto sušenje na prirast. Zahvaljujući financijskim sredstvima Zavoda za šumarska istraživanja šumarskog fakulteta u Zagrebu bilo mi je omogućeno istraživanje spomenutog problema. S obzirom na to da sam se već prethodnih godina bavio sličnom problematikom, bilo samoinicijativno, bilo kao suradnik Instituta za šumarska istraživanja SRH, ovaj rad predstavlja u neku ruku nastavak mojih prethodnih studija. Zato je razumljivo, da sam kao objekt istraživanja izabrao gospodarsku jedinicu »Belevine« u Gorskom Kotaru, tj. onu istu acidofilnu jelovu šumu (Abieteto-Blechnetum Horvat) koja je bila predmet višestrukih istraživanja pa je u Šumarskom listu, Glasniku za šumske pokuse i drugdje već detaljno opisana. Do sada raspolažemo vrlo različitim i vrijednim podacima mjerenja i opažanja za tu fakultetsku šumu. Kako je bila istovremeno izvrgnuta različitim napadajima, počevši od imele (Viscum album f. sp. abietis Tub.) pa do jelova moljca (Argyresthia fundella F. R.) i ostalih defolijatora, odlučio sam na tom objektu usredotočiti opažanja i mjerenja, kako bih uzmogao odgovoriti na postavljeno pitanje. METODA RADA Na veličinu prirasta utječu različiti faktori. Vrlo je teško izolirati jedan faktor i istražiti samo njegov utjecaj. U našim istraživanjima imamo baš takav slučaj: treba istražiti kakvu je reperkusiju imalo sušenje jelika na njihov prirast. Kako su u posljednjemu, masovnom napadaju na jelike sudjelovali uglavnom defolijatori, mislio sam da će biti najbolje ako se najprije utvrdi koliko je smanjena asimilacijska površina napadnutih jelika. U tu svrhu opisao sam posebnu metodu rada: »Kako utvrditi postotak smanjenja asimilacijske površine u zaraženim jelovim šumama?«, koja je publicirana u Šumarskom listu br. 7—8 od 1970. godine. Po toj metodi utvrdio sam postotak smanjenja asimilacijske površine u cijeloj gospodarskoj jedinici »Belevine« u mjesecu svibnju 1969. godine. Podatke o tome prenosim iz spomenutog broja Šumarskog lista. Ako se površine pojedinih odjela uzmu kao težine, dobiva se prosječni postotak smanjenja asimilacijske površine za gospodarsku jedinicu »Belevine «. On iznosi oko 7%. Dvije godine kasnije, tj. početkom srpnja 1971. primijenio sam istu metodu rada i utvrdio postotak smanjenja asimilacijske površine u iznosu od |
ŠUMARSKI LIST 1-2/1972 str. 45 <-- 45 --> PDF |
Smanjenje asimilacijske Šumski predjel Odjel Površina ha površine u % VII, 1 a 11,3 6 VII, 1 b 21,5 7 VII, 1 c 19,7 5 VII, 1 d 23,2 10 VII, 1 e 8,7 5 VII, 1 f 18,4 7 VII, 2 a 22,4 7 VII, 2 b 25,0 7 VII, 2 c 22,1 8 VII, 3 a 17,6 7 VII, 3 b 18,6 6 VII, 3 c 18,1 7 VII, 4 a 12,7 13 VII, 4 b 21,0 7 VII, 4 c 11,2 8 Ukupno : 271,15 9%. Ta je brojka izračunana na temelju mjerenja, koje se sastojalo u tome da je u gospodarskoj jedinici »Belevine« položeno 13,550 km pruga širine od 10 metara, što će reći 13,55 ha pruga ili oko 5% od ukupne površine gospodarske jedinice (271,15 ha). Na tim prugama mjereni su prsni promjeri svih stabala iznad taksacijske granice od 10 cm. No, pored toga dalekozorom su motrene krošnje svakoga izmjerenog stabla i pritom je ocjenjivan gubitak iglica u postocima od 0 do 100, gdje 0 znači zdravo stablo, a 100 suho jelovo stablo bez iglica; 10% znači da je uništeno 10% iglica, odnosno da sadašnja asimilacijska površina iznosi 0,9 u odnosu na punu krošnju, 20% znači da je uništeno 20% iglica itd. Za tu svrhu konstruirao sam posebni manual u obliku tabele 1, navedene u spomenutom broju Šumarskog lista. Da bi se mogao istovremeno utvrditi prirast pojedinih jelovih stabala i cijele šume, bušena su svrdlom sva jelova stabla koja su pala u vizurni pravac (kod iskolčenja pruge busolom). Sa svakoga jelova stabla uzet je po jedan izvrtak, koji je umotan u papirić na kojem je bio upisan broj odjela, prsni promjer stabla i % smanjenja asimilacijske površine bušenog stabla. U svemu je uzeto 695 uzoraka (izvrtaka) sa 695 jelovih stabala, kako slijedi: 326 izvrtaka s 326 jelovih stabala potpune krošnje; 230 izvrtaka s 230 jelovih stabala, kojima je krošnja smanjena za 10%; 95 izvrtaka s 95 jelovih stabala, kojima je krošnja smanjena za 20%; 33 izvrtaka s 33 jelovih stabala, kojima je krošnja smanjena za 30%; 9 izvrtaka s 9 jelovih stabala, kojima je krošnja smanjena za 40%; 2 izvrtka s 2 jelova stabla, kojima je krošnja smanjena za 50%; 695 izvrtaka ukupno. |
ŠUMARSKI LIST 1-2/1972 str. 46 <-- 46 --> PDF |
U drugom obliku to izgleda ovako: 1 X 326 = 326.0 0.9 X 230 = 207.0 56.5. Ta razlika daje podatak o smanjenju asimilacijske površine koji 0.8 X 95 = 76.0 0.7 X 33= 23.1 0,6 X 9 = 5.4 0.5 X 2 = 1.0 638.5 Brojka od 638.5 znači sadašnje stanje asimilacijske površine. Akostanje usporedimo sa stanjem prije oštećenja (695) dobit ćemo razliku to od namu postotku (p) iznosi: 56.5 p = 100 = 8% 695 To bi značilo, da je u gospodarskoj jedinici »Belevine« asimilacijska površina smanjena za oko 8%. Slični podatak dobili smo na temelju potpunijeg obračuna uzevši u obzir sva izmjerena stabla na prugama, gdje je situacija bila ovakva: 3.368.9 znači stanje asimilacijske površine početkom srpnja 1971; stanje prije oštećenja 3.702. Razlika je 333.9 ili 8.9%. To znači da su uzorci (izvrtci) dobri reprezentanti stanja šume, što je razumljivo, jer su primjerne pruge položene po principu slučajnosti. Ako usporedimo podatke o smanjenju asimilacijske površine ljeti 1969. sa stanjem 1971, vidimo da se ne radi o signifikantnim razlikama. Prema tome, može se reći da se stanje u gospodarskoj jedinici »Belevine« nije pogoršalo, odnosno da sušenje jele ovdje nema progresivni karakter. No, ipak se radi o šumi gdje je asimilacijska površina jele — uzevši u prosjeku — smanjena za oko 8—9%. Budući da smo tako utvrdili stanje objekta i uzeli priličan broj reprezentativnih uzoraka, postoji mogućnost za različite analize i različita razmatranja. Ograničio sam se na ove probleme: 1. kako prirašćuju zdrava i zaražena jelova stabla; 2. kada je debljinski prirast jele počeo padati; 3. kako utječe smanjenje asimilacijskog aparata na prirast stabla. U tu svrhu izvrći su analizirani na različite načine. Prvo: na svakom izvrtku izmjereno je individualno vrijeme prijelaza (t) za debljinske stupnjeve od 5 cm (v. si. 1). Drugo: na svakom je izvrtku izmjeren debljinski prirast za proteklih 10 godina, tj. od 1961—1970. (v. si. 2). Treće: na svakom je izvrtku izmjeren debljinski prirast za proteklih 5 godina, tj. od 1966—1970. (v. si. 3). Četvrto: na svakom je izvrtku izmjeren debljinski prirast u tijeku prethodnih proteklih 5 godina, tj. od 1961—1965. (v. si. 3). Nakon četverostruke analize izvrtaka obavljeno je sortiranje izvrtaka, te njihovo izravnavanje po teoriji najmanjih kvadrata. |
ŠUMARSKI LIST 1-2/1972 str. 47 <-- 47 --> PDF |
ml i I milllUMHfJ 2´5 cm t = 12´5 godina Si-Fig. I 1971 \197C 1961 ™ mm ri im i nune *» SI.-Fig. 2. 1971 1970 ms 119P5 1961 m llPfit ill ^wkw^MMMitMi k-—^i^— Si- s2 — SI.-Fig. 3. |
ŠUMARSKI LIST 1-2/1972 str. 48 <-- 48 --> PDF |
REZULTATI Vrijeme prijelaza U tijeku ljeta 1959. godine izradio sam sa svojim studentima — za vrijeme terenske nastave — gospodarsku osnovu za šumu Belevine (1959 — 1968. godine). Tom prilikom (2. i 3. VI 1959.) izbušili smo u spomenutoj gospodarskoj jedinici 1255 izvrtaka s 1255 jelovih stabala. Volumni prirast smo obračunali po metodi »Tablice postotka prirasta« (v. Šumarski list, Zagreb 1954.) uz pomoć medijana individualnih vremena prijelaza. Početkom mjeseca srpnja 1971. godine ponovno su studenti Zagrebačkoga šumarskog fakulteta izbušili na istom objektu priličan broj izvrtaka — njih 695 sa 695 stabala. Pritom su sudjelovali i moji suradnici mr Š im e Meštrović, dipl. ing. šumarstva i Radovan Križance, dipl. ing. šumarstva, sveučilišni asistenti. Kao i prije 11 godina, i ovaj je puta obračunana medijana individualnih vremena prijelaza. Zanimljiva je usporedba podataka iz 1959. i onih 11 godina kasnije. Evo te komparacije. Tabela 1 Medijana individualnih vremena prijelaza Median of individual recruitment times D/cm 1959. godine 1971. godine D. b. h./cm. Year 1959 Year 1971 12.5 28 18 17.5 24 26 22.5 22 23 27.5 18 20 32.5 16 16 37.5 16 15 42.5 14 15 47.5 15 16 52.5 14 13 57.5 12.5 14 62.5 14 13 67.5 12 13.5 72.5 14 12 77.5 12 10.5 82.5 13 12.5 87.5 9 7 92.5 — 14.0 97.5 — 27 Odmah upada u oči da velikih razlika nema, a to bi značilo, da je debljinski prirast pa i postotak prirasta ostao skoro isti. Ipak nije tako! Razlog leži u medijan i individualnih vremena prijelaza. Koliko god ima medijana pri obračunu prirasta svojih velikih prednosti, u ovom slučaju nam ne odgovara, jer nisu došla do izražaja dulja individualna vremena prijelaza u posljednjih 10 godina. Bolji uvid dala bi nam aritmetička odnosno harmonična sredina. No, kako se s vremenima prijelaza ne obuhvača isto |
ŠUMARSKI LIST 1-2/1972 str. 49 <-- 49 --> PDF |
vremensko razdoblje, odustao sam od daljnje obrade vremena prijelaza; prešao sam na analizu i izračunavanje debljinskog prirasta najprije za vremenski interval od 1961—1970. godine, a onda za vremenske intervale od 1961—1965. te od 1966—1970. Godišnji debljinski prirast zdravih jelovih stabala u usporedbi s prirastomjelovih stabala, kojima je asimilacijska površina smanjena Sve uzorke (izvrtke) podijelio sam u dvije grupe odnosno u dva kolektiva. Prvi kolektiv obuhvatio je sve uzorke izbušene iz zdravih jelovih stabala. Drugi kolektiv su uzorci izbušeni s jelovih stabala kojima je asimilacijska površina smanjena. Radi jednostavnosti, prvi ćemo kolektiv zvati »zdrava«, a drugi »zaražena jelova stabla«. Analiza izvrtaka obavljena je onako, kako je već navedeno i prikazano na slici 2. Prosječni godišnji debljinski prirast izračunan je po debljinskim stepenima prema formuli: šs 1 Zd = 2 , 10 b gdje (S3) znači širinu posljednjih 10 godova; (b) je broj uzoraka. Tabela 2 Prosječni godišnji debljinski prirast jele u tijeku 1961—1970. godine u milimetrima Average annual diameter increment of Fir for the years 1961—1970. in mm. zdravih jelovih stabala zaraženih jelovih stabala Healthy Fir trees Infested Fir trees D/cm D/cm D.b.h/cm. Z Z´ Z´r D.b.h./cm. zr 12.5 2.60 2.32 2.46 1.64 12.5 17.5 3.26 2.82 1.62 2.09 17.5 22.5 2.22 3.26 2.87 2.44 22.5 27.5 4.68 3.64 2.04 2.81 27.5 32.5 4.76 3.96 2.97 3.08 32.5 37.5 3.68 4.22 3.50 3.27 37.5 42.5 3.71 4.42 3.36 3.40 42.5 47.5 3.70 4.56 2.58 3.47 47.5 52.5 4.40 4.64 2.96 3.47 52.5 57.5 4.27 4.66 3.42 3.40 57.5 62.5 4.18 4.62 3.69 3.27 62.5 67.5 4.03 4.52 3.27 3.07 67.5 72.5 4.86 4.36 3.56 2.81 72.5 77.5 4.26 4.14 4.00 2.48 77.5 82.5 6.56 3.86 2.60 2.09 82.5 87.5 4.80 3.52 1.63 87.5 92.5 3.40 3.12 1.11 92.5 97.5 1.20 0.52 97.5 |
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Rezultati analize i obračuna nalaze se u tabeli 2 pod oznakom (Z) i (Z´), gdje (Z) znači prosječni godišnji debljinski prirast zdravih, a (Z´) zaraženih jelovih stabala tijekom vremenskog intervala od 1961—1970. godine. U istoj tabeli oznake (Zr) i (Z´r) znače izravnane prosječne godišnje debljinske priraste. Godišnji debljinski prirast zdravih jelovih stabala u gospodarskoj jedinici »Belevine« može se izraziti jednadžbom (1): Zr = —0.001203 D2 + 0.136334 D + 0.800815 (1) Godišnji debljinski prirast zaraženih jelovih stabala može se izraziti jednadžbom (2): Z´r = —0.001311 D2 + 0.131027 D + 0.202656 (2) Na slici 4 prikazan je tijek godišnjega debljinskog prirasta jelovih zdravih i zaraženih stabala. Iz te slike kao i iz tabele 2 vidi se vrlo jasno, kako »zaražena« jelova stabla slabije prirašćuju. Uzevši u račun broj izvrtaka po debljinskim stupnjevima, izračunali smo da je prirast zaraženih jelovih stabala za 36% manji od prirasta zdravih jelovih stabala. Navedena konstatacija vrlo je važna, jer nam daje uvid u ekonomske gubitke u napadnutim šumama. No, pored tako globalno utvrđenog gubitka na prirastu, bilo bi zanimljivo utvrditi funkcionalnu zavisnost padanja prirasta od stupnja zaraze ili, bolje rečeno, od smanjenja asimilacijske površine. Prije nego što prijeđemo na rješavanje toga problema, pokušat ćemo odgovoriti na pitanje, kad je nastupilo opadanje debljinskog prirasta. Godišnji debljinski prirast jele u različito vrijeme Kako je u metodi rada već spomenuto, svaki izvrtak analiziran je četiri puta. Treća analiza odnosi se na mjerenje prosječnoga godišnjeg debljinskog prirasta jele za vremenski interval od 1966—1970. Taj prirast izračunan je po formuli: ši 1 Zj = 2 5 b Četvrta analiza odnosi se na mjerenje prosječnoga godišnjeg debljinskog prirasta jele za vremenski interval od 1961—1965. Taj je prirast izračunan po formuli: Š2 1 Z2 = 2 5 b 4fi |
ŠUMARSKI LIST 1-2/1972 str. 51 <-- 51 --> PDF |
Tabela 3 Prosječni godišnji debljinski prirast jele u milimetrima Average annual diameter increment of Fir in mm. u tijeku 1966—1970. godine u tijeku 1961—1965. godine For the years 1966—1970 For the years 1961—1965 D/cm D/cm D.b.h./cm. Zi Zir Z2 Z2r D.b.h./cm. 12.5 2.56 2.82 2.64 2.75 12.5 17.5 3.28 3.06 3.25 3.05 17.5 22.5 2.32 3.27 2.12 3.34 22.5 27.5 4.64 3.46 4.72 3.60 27.5 32.5 4.60 3.63 4.92 3.85 32.5 37.5 3.46 3.77 3.90 4.07 37.5 42.5 3.45 3.89 3.97 4.27 42.5 47.5 3.42 3.99 3.98 4.46 47.5 52.5 4.11 4.06 4.69 4.62 52.5 57.5 4.07 4.11 4.48 4.77 57.5 62.5 4.06 4.14 4.31 4.89 62.5 67.5 3.46 4.14 4.60 4.99 67.5 72.5 4.57 4.12 5.16 5.08 72.5 77.5 3.72 4.08 4.80 5.14 77.5 82.5 6.20 4.02 6.93 5.18 82.5 87.5 2.80 3.93 6.80 5.20 87.5 92.5 3.60 3.82 3.20 5.21 92.5 97.5 3.67 5.19 97.5 Rezultati o tim prirastima nalaze se u tabeli 3. (Zi) i (Z2) znače izmjereni, a (Zir) i (Z2r) izravnani debljinski prirasti. Na temelju obračuna po teoriji najmanjih kvadrata izrazio sam prosječni godišnji debljinski prirast jele u vremenu od 1966—1970. jednadžbom (3), a u vremenu od 1961—1966. jednadžbom (4). Zir = —0.000461 D2 + 0.060856 D + 2.135759 (3) Z2r = —0.000402 Da + 0.073009 D + 1.896828 (4) Na slici 5 prikazane su te jednadžbe. Iz podataka u tabeli 3 i iz slike 5 jasno se vidi, da je debljinski prirast jele pao za preko 15% u vremenskom intervalu od 1966—1970. godine. Pošto smo utvrdili da je u proteklih 5 godina nastupilo izrazito padanje prirasta, sada nas zanima koje je godine ono bilo najizrazitije. Analiza izvrtaka pokazala je, da su godovi bili najuži u 1968. i 1969. godini. U stvari, tada je istraživana šuma imala »bolesni« i zabrinjavajući izgled. Usput spominjemo, da se danas stanje šume popravilo pa je ljeti 1971. zabilježen nezapamćen urod jele. |
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PROSJEČNI GODIŠNJI DEBLJINSKI PRIRAST ZDRAVIH (Zr ) I ZARAŽENIH (Z´r) JELOVIH STABALA U TOKU 1961-1970 GODINE Average annual diameter increment of healty (Zr) and infested Fir trees (Z´r) for the years 1961-1970 Gospodarska jedinica Management unit „BELE VINE" Mjereno: srpnja 1971 Measure´d: July, 1971 125 175 225 275 325 375 425 475 525 575 625 675 725 775 625 675 925 975 0 Cm D.b.h/am. St.-Fig. 4. DISKUSIJA Prvo pitanje na koje treba odgovoriti glasi: »Nisu li možda klimatski faktori prouzrokovali smanjenje debljinskog prirasta?«. Da bismo odgovorili na to pitanje, posegnuli smo za onim klimatskim podacima kojima raspolažemo za meteorološke stanice Zalesina i Delnice. To su podaci o oborinama i temperaturama koji su prikazani u tabelama 4 i 5. Iz tih tabela sam izračunao, da je u tijeku od 5 godina, tj. od 1966—1970. god. palo 10.660 mm kiše ili godišnje 2.132 mm; za isto vrijeme palo je u tijeku vegetacijske periode 5.150 mm ili godišnje 1.030 mm. Tijekom periode od 1961—1965. palo je ukupno 10.800 mm ili godišnje 2.160 mm kiše, a za isto vrijeme u tijeku vegetacijske periode 5.033 mm ili godišnje 1.006 mm. Evidentno je, da |
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se vremenski intervali 1961—1965. te 1966—1970. ne razlikuju po oborinama. Ako posebno pogledamo godine 1968. i 1969, vidjet ćemo da one ne odstupaju od prosjeka. Prema tome je jasno, da se oborinama ne može pripisati smanjenje debljinskog prirasta u posljednjih 5 godina. Ni razlike u temperaturama nisu takve da bi mogle prouzrokovati spomenuto padanje prirasta. PROSJEČNI GODIŠNJI DEBLJINSKI PRIRAST JELE U TOKU 1961 -1965. GODINE (Z2) i 1966-1970. GODINE tZ,) # ´mm Average annual diameter increment for th years 1961-1965 (Z2),and s 1966- 1970 (Z,) *J - Z< Gospodarska jedinica Management unit „BELEVINE" Mjereno: srpnja 1971. Measured: July, 1971 i i i i i i i i i i > J I U_ I ,. 125 175 225 275 325 375 iZS 475 525 573 625 675 725 775 625 375 92 5 STSDcmakryim. Sl.-Flg. 5. Što se tiče gospodarskih mjera (sječa), treba istaknuti da se u gospodarskoj jedinici »Belevine« siječe godišnje oko 2.500 m3, koliko po prilici iznosi godišnji prirast. Sječa se obavlja pod znanstvenim rukovodstvom stručnjaka sa Šumarskog fakulteta pa se ni gospodarskim zahvatima ne bi moglo pripisati smanjenje prirasta jele; što više, trebalo bi očekivati njegovo povećanje. Prema tome se prilično pouzdano može reći, da su određeni štetnici (možda i gljive) prouzrokovali smanjenje prirasta koje sam utvrdio. Ento 51 II I |
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DEBLJINS Diameter OPADANJE DEBLJINSKOG PRIRASTA SA SMANJENJEM ASIMILACIJSKE POVRŠINE JELE Falling-off of diameter increment with the reduction of assimilating surface of Fir %J N N (S) c L ^r a» 100 75 50 / GCGOSPODARSKA JEDINICA 25 Management unit „BEL EVINE" MJERENO: SRPNJA 1971. y i_. i i i i i Measured: July, 1971 J 1 . ,—_—^ 05 06 07 0´8 09 10 KROŠNJA-Crown S(.-F/g. 6. molozi i zaštitari već su dali i dat će detaljno tumačenje o kojim se štetnicima radi. A sada pokušajmo odgovoriti na treće pitanje: »Kako utječe smanjenje asimilacijskog aparata na prirast?«. Kako pada debljinski prirast sa smanjenjem asimilacijske površine Da uzmognem odgovoriti na navedeno pitanje, razvrstao sam uzorke po grupama: 0%, 10%, 20%, 30%, 40°/o itd., gdje 0 znači uzorke s jelovih stabala normalne asimilacijske površine, 10% znače stabla kod kojih je asimi |
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lacijska površina smanjena za 10%, 20% znače stabla kod kojih je asimilacijska površina smanjena za 20%, itd. Na izvrcima smo izmjerili godišnji debljinski prirast u tijeku proteklog petogodišta od 1966—1970. Nakon varijacijsko- statističke obrade podataka dobio sam ove rezultate: Gubitak iglica 0% 10% 20% 30% 40«/0 50% b 326 230 95 33 9 2 d3 50.1 45.8 41.3 45.1 30.8 15.0 cm. Z„ 3.82 2.86 2.76 2.38 2.37 1.30 mm. (b) označuje broj uzoraka; (ds) srednji promjer jelova stabla; (Zs) prosječni godišnji debljinski prirast u tijeku vremenskog intervala od 1966—1970. Ako pogledamo dobivene rezultate, vidimo kako debljinski prirast pada sa smanjenjem asimilacijske površine jelova stabla. Kod zdravih jelovih stabala s nesmanjenom krošnjom, prosječni godišnji debljinski prirast iznosio je 3,82 mm, da bi pao na iznos od 2,86 mm kod stabala kojima je asimilacijska površina smanjena za 10%, a na iznos od 2,76 mm kod stabala kojima je asimilacijska površina smanjena za 20%, itd. Odmah upada u oči, da padanje debljinskog prirasta nije linearno, jer je smanjenje iglica od 10% prouzrokovalo padanje prirasta za 20%. Na žalost, u grupama 30%, 40% i 50°/o nemamo veliki broj uzoraka, jer ih u istraživanom objektu nije bilo u dovoljnoj mjeri. Na tom se objektu intenzivno gospodari, pa se relativno brzo uklanjanju stabla koja su izgubila više od 20 postotaka iglica. Zato će se naša istraživanja nastaviti u onim šumama gdje je sušenje zauzelo veći mah. Bilo kako bilo, na temelju provedenih istraživanja vidi se da smanjenje asimilacijske površine od 10% prouzrokuje smanjenje debljinskog prirasta ne za isti iznos od 10%, kako bi se to na brzinu zaključilo, nego mnogo više. Radi ilustracije navodim ovdje grafikon na slici 6, koji sam konstruirao na temelju ovih istraživanja. Na apscisnoj osi nanesene su asimilacijske površine stabala, gdje 1 znači normalnu asimilacijsku krošnju, 0.9 znači asimilacijsku krošnju smanjenu za 10%, 0.8 asimilacijsku krošnju smanjenu za 20% itd., a 0 znači stabla bez ijedne iglice. Na ordinatnoj osi naneseni su godišnji debljinski prirasti (Zs) u zavisnosti o asimilacijskoj površini, izraženi u relativnoj mjeri. ZAKLJUČAK Sušenje jelovih šuma imalo je za posljedicu padanje prirasta. U acidofilnoj šumi (Abieteto-Blechnetum, Horvat) »Belevine« u Gorskom Kotaru utvrđeno je mjerenjima, da je debljinski prirast jele pao u vremenu 1966— 1970. Najveće smanjenje toga prirasta zabilježeno je 1968. i 1969. godine poslije čega se prirast popravio. Spomenuto padanje prirasta pripisuje se šumskim štetnicima, defolijatorima, koji su masovno napali jelove šume. Komparacijom debljinskog prirasta zdravih i zaraženih jelovih stabala utvrđen je ovim pokusom u prosjeku pad prirasta za oko 30% na zaraženim stablima. |
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Zaražena stabla izgubila su određenu količinu iglica. Navedenim se istraživanjima došlo do zaključka, da smanjenje asimilacijske površine prouzrokuje padanje debljinskog prirasta, koje smo za istraženi objekt mogli izraziti eksponencijalnom krivuljom na slici 6, gdje x = 1 označuje potpunu krošnju; x = 0.9 krošnju u kojoj nedostaje 10% iglica; x = 0.8 označuje krošnju koja je izgubila 20% iglica itd., a 0 označuje stablo bez ijedne iglice. Iz spomenute krivulje vidi se ovo: — ako je asimilacijska površina smanjena za 10% debljinski prirast pada za 20% — ako je asimilacijska površina smanjena za 20% debljinski prirast pada za 35% — ako je asimilacijska površina smanjena za 30% debljinski prirast pada za 45% — ako je asimilacijska površina smanjena za 40% debljinski prirast pada za 55% itd. itd. To je prvi rezultat istraživanja samo na jednom objektu. Istraživanja će se nastaviti na drugim objektima i u drugim uvjetima, da bi se mogla utvrditi zakonitost. Investigations of the effect of defoliators on the increment of Fir forests Withih the framework of complex investigations on »The epidemic dieback and drying of Silver Fir (Abies alba Mill.)« my role was among other things to investigate what repercussions the mentioned dieback had on the increment. Thanks to the financial funds of the Institute of Forest Research, Faculty of Forestry, Zagreb, it was possible for me to investigate the mentioned problem. Taking into consideration that already in previous years I was concerned with similar problems — either on my own initiative or as a collaborator of the Institute of Forest Research of the S. R. od Croatia — this paper represents in some measure a continuation of my previous studies. Therefore it is quite understandable that as the object of my research I chose the management unit of »Belevine« in the Gorski Kotar region (Croatia), i. e. the same acidophilus Fir forest (Abieto-BlechnetumHorvat) which has been the subject of repeated investigations, and was described in detail in Šumarski list (Forestry Review), Glasnik za šumske pokuse (Annals for Forest Research) etc. So far we have at our disposal very different and valuable data of measurements and observations regarding this faculty demonstration forest. As it was simultaneously subjected to various attacks, beginning with mistletoe (Viscum album f. sp. abietis Tub.) to the Fir needle moth (Argyresthia fundella F. R.), and other defoliators, I decided to focus my observations and measurements on this forest in order to give an answer to the query under discussion. The magnitude of increment is influenced by various factors. It is very difficult to isolate but one factor and to investigate its effect only. In the present investigations we have exactly to deal with such a case: it is neccessary 54 |
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to find out what repercussion had the dieback of Fir stands on their increment. Considering that in the last mass attack chiefly defoliators took part, I thought it would be best to establish first how much the assimilating´ surface of attacked Fir stands was reduced. To this purpose I described a special working method, which was published in »šumarski list« No 7/8, 1970 under the title of »How to determine the percentage decraase of assimilation area in infested Silver Fir Forests?«. According to this method I found out the percentage of reduction of assimilating surface in the whole management unit of »Belevine« in the month of May, 1969. I take the data about this from the mentioned number of šumarski list. Reduced assimilating Forest district Compartment No. Area ha surface in % VII, 1 a 11,3 6 VII, 1 b 21,5 7 VII, 1 c 19,7 5 VII, 1 d 23,2 10 VII, 1 e 8,7 5 VII, 1 f 18,4 7 VII, 2 a 22,4 7 VII, 2 b 25,0 7 VII, 2 c 22,1 8 VII, 3 a 17,6 7 VII, 3 b 18,6 6 VII, 3 c 18,1 7 VII, 4 a 12,7 13 VII, 4 b 21,0 7 VII, 4 c 11,2 8 Total : 271,15 If the areas of individual compartments are taken as weights, we obtain the average percentage of reduction of the assimilating surface for the management unit of »Belevine«. It amounts to about 7%. Two years later, i. e. at the beginning of July, 1971, I applied the same working method and established the percentage of reduction of the assimilating surface to be 9%. This figure was computed on the basis of measurements, which consisted in that in the management unit of»Belevine« were laid out 13.550 km of sample-strips 10 m. wide making a total of 13.55 ha. sample-strips, or about 5% of the total area of the management unit (271.15 ha.). On these strips were measured the breast height diameters (d. b. h.) of all trees above the minimum measurement limit of 10 cm. In addition to this there were observed by means of a field-glass the crowns of each measured tree and was estimated the loss of needles in percents from 0 to 100, where 0 means a healthy Fir tree and 100 a dead one without needles; 10% means that there were destroyed 10% of needles, or that the actual assimilating surface amounts to 0.9 in relation to the full crown, 20% means |
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that 20% of needles were destroyed, etc. To this purpose I constructed a special form in the shape of Table 1 presented in the mentioned number of Šumarski list. In order to make possible at the same time the determination of increment of individual trees and of the whole forest, there were made borings on all Fir trees which fell into the line of sight (when laying out strips by compass). From each Fir tree was taken one increment core, which was wrapped into a piece of paper on which was recorded the compartment number, diameter b. h. and percentage of reduction of assimilating surface on the bored tree. There were taken in all 695 samples (cores) from as many Fir trees, as follows: 326 cores from 326 Fir trees with full crown; 230 cores from 230 Fir trees with crown reduced by 10%; 95 cores from 95 Fir trees with crown reduced by 20%; 33 cores from 33 Fir trees with crown reduced by 30%; 9 cores from 9 Fir trees with crown reduced by 40%; 2 cores from 2 Fir trees with crown reduced by 50%; 695 cores in total Another variant of presentation would be as follows: 1 X 326 = 326.0 0.9 X 230 = 207.0 0.8 X 95 = 76.0 0.7 X 33 = 23.1 0.6 X 9 = 5.4 0.5 X 2 = 1.0 638.5 The figure 638.5 means the present state of the assimilating surface. If this state is compared with the state before damage (695) we obtain a difference of 56.5. This difference gives us information about the reduction of the assimilating surface, which in percents amounts to: 56.5 p = 100 = 8% 695 Which would mean that in the management of »Belevine« the assimilating surface is diminished by about 8%. We obtained a similar data on the basis of a more complete calculation taking into consideration all measured trees on strips, where the situation was as follows: 3,368.9 means the state of assimilating surface at the beginnig of July, 1971; the state before damage was 3,702. The difference is 333.9 or 8.9%. Which means that the samples (cores) are good representatives of the condition of the forest, which is understandable, because the sample-strips were laid out according to the principle of random sampling. |
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If we compare data about the reduction of assimilating surface in 1969 with those of 1971, we see that the differences are not significant. Accordingly we may say that the state in the management unit of »Belevine« did not worsen, or that the dieback of Fir there did not have a progressive character. Nevertheless, we are dealing with a forest where the assimilating surface of Fir — taken on an average — was reduced by about 8—9%. Having thus determined the state or the area in question and taken a considerable number of representative samples, there exists a possibility for different analyses and considerations. I restricted myself to the following problems: 1. How do healthy and infested trees put on their increment? 2. When did the diameter increment of Fir begin to fall off? 3. How does the reduction of assimilating apparatus affect the tree increment? To this purpose the increment cores were analysed in different ways. First, on each core was measured the individual recruitment time (t) for 5 cm. — diameter sub-classes (see Fig. 1). Second, on each core was measured the diameter increment for the past 10 years, i. e. from 1961—1970 (see Fig. 2). Third, on each core was measured the diameter increment for the past 5 years, i. e. from 1966—1970 (see Fig. 3). Fourth, on each core was measured the diameter increment during the previous past years, i. e. from 1961—1965 (see Fig. 3). After a fourfold analysis of cores a sorting of cores was carried out and the resulting data smoothed according to the theory of least squares. Recruitment time In the course of the summer of 1959 I worked out together with my students — during the field teaching — a working plan for the forest of »Belevine« (1959—1968). On this occasion we extracted in the mentioned management unit 1,225 increment cores from as many Fir trees. The volume increment was computed according to the method of »Increment percentage tables« with the help of the median of individual recruitment times (see Šumarski list, Zagreb 1954). At the beginning of July, 1971, students of the Zagreb Forestry Faculty extracted repeatedly in the same forest a considerable number of increment cores, viz. 695 from 695 Fir trees. On this occasion took part aslo my collaborators Šime Meštrović, M. F. and graduate engineer, and Radovan Križance , graduate engineer of forestry, both of them University assistants. Like 11 years ago, so this time the median of individual recruitment times was computed. It is interesting to compare the data from 1959 with data obtained 11 years later (see Tab. 1). What catches our eye immediately is that there are no great differences, which would mean that the diameter increment and the increment percent remained almost the same. But it is not so! The reason lies in the median of individual recruitment times. Although the median has its great adventages when calculating the increment, in this case it is not suitable, because the 57 |
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longer individual recruitment times in the last lo years have not come into evidence. But as the recruitment times did not include the same period of time, we desisted from further treatment of the recruitment time; we passed to an analysis and calculation of the diameter increment, first for the 1961—1970 time interval, then for the 1961—1965 and 1966—1970 time intervals. Annual diameter increment of healthy Fir trees as compared wit the increment of Fir trees whose assimilating surface was reduced All samples (cores) were divided into two groups or collectives. The first collective included all samples extracted from healthy Fir trees. The second collective contained samples extracted from Fir trees whose assimilating surface was reduced. For the purpose of simplification the first collective will be called »healthy«, and the second »infested Fir trees«. The analysis of increment cores was performed in the manner already mentioned and shown in Fig. 2. The average annual diameter increment was computed after the formula: š3 1 Zd - 2 , 10 b where (š3) means the width of the last 10 growth-rings, and (b) the number of samples. The results of analysis and computation are given in Tab. 2 under designation (Z) and (Z´), where (Z) means the average annual diameter increment of healthy and (Z´) of infested Fir trees during the 1961—1970 time interval. In the same table the designations (Zr) and (Z´r) mean the smoothed average annual diameter increments. The annual diameter increment of infested Fir trees in the management unit of »Belevine« may be expressed by equation (1): Zr = —0.001203 Da + 0.136334 D + 0.800815 (1) The annual diameter increment of infested Fir trees may be expresse by equation (2): Z´r = —0.001311 D2 + 0.131027 D + 0.202656 (2) In Fig. 4 is represented the course of the annual diameter increment of healthy and infested trees. From this figure and from Tab. 2 it is clearly visible that »infested« Fir trees put on a lower increment. Taking into calculation the number of cores according to diameter sub-classes, we found that the increment of infested Fir trees was by 30% lower than the increment of healthy Fir trees. This finding is very important, because it gives us an insight into the economic losses in the forests attacked. But, in addition to such a global |
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determination of increment losses, it would be interesting to establish a functional interdependence between the falling-off of increment and the degree of infestation, or, properly speaking, of the reduction of assimilating surface. Before solving this problem, we shall make an attempt at giving an answer to the query when the falling-off of increment had set in? Annual diameter increment of Fir at different times As has already been mentioned in the chapter on the Working Method, each increment core was analysed four times. The third analysis relates to the measurement of the average annual diameter increment of Fir for the 1966—1970 time interval. This increment was computed according to the formula: ši 1 Zi = 2 5 b The fourth analysis relates to the measurement of the average annual diameter increment of Fir for the 1961—1965 time interval. This increment was computed according to the formula: Š2 1 Z2 = 2 5 b The results concerning these increments are found in Tab. 3. (Zi) and (Zo) mean the measured increments, while (Zir) and (Zar) mean the smoothed diameter increments. On the basis of the computation according to the theory of least squares, I expresed the average diameter increment of Fir for the 1966—1970 time interval by equation (3), and for the 1961—1966 time interval by aquation (4). Zlr = —0.000461 D* + 0.060856 D f 2.135759 (3) Z2r = —0.000402 D2 + 0.073009 D + 1.896828 (4) These equations are represented in Fig. 5. From data in Tab. 3 and Fig. 5 it is clearly visible that diameter increment of Fir fell off by over 25% during the 1966—1970 time interval. Having established that in the past 5 years a marked falling-off of increment had set in, we are now interested to know what year it was most marked. An analysis of the cores showed that the growth rings were narowest in 1968 and 1969. In fact, at that time the studied forest had a »diseased« and alarming appearance. Let us state by the way that to-day the condition of the forest has improved, and that in the summer of 1971 an unheard-of cone crop was recorded. The first query to which we should lend an ear is: »Did the climatic factors not cause perhaps the reduction of the diameter increment?« In |
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order to answer this question we had to resort to those climatic data which we have at our disposal from the weather stations Zalesina and Delnice. These data about the rainfall and temperatures are presented in Tabs. 4 and 5. From these tables we computed that in the course of 5 years, i. e. from 1965 to 1970, the amount of rainfall was 10,660 mm. or annually 2,132 mm.; for the same time period the rainfall in the course of the growing season was 5,150 mm. or annually 1,030 mm. During the 1961—1965 period the amounth of rainfall totalled 10,880 mm. or annually 2,160 mm., while for the same time in the course of the growing season it was 5,033 mm. or annually 1,066 mm. It is evident that the time intervals of 1961—1965 and 1966—1970 did not differ as regards rainfall. If we study separately the years 1968 and 1969, we see that they did not deviate from the average. Consequently, we cannot ascribe to the rainfall the reduction of diameter increment in the last 5 years. Neither are the differences in temperatures such as to cause the mentioned reduction of increment. With regard to the management measures (fellings) it ought to be stressed here that in the management unit of »Belevine« the annual cut is ca. 2.500 cu. m., which is approximately as much as the annual increment. The cutting is performed under the scientific gudiance of specialists from the Faculty of Forestry, and thus the management interventions could not be accounted for the reduction of increment of Fir either, but, what is more, we should expect it to increase. Accordingly, it may be said rather reliably that certain pests caused the reduction of increment which we had established. Entomologists and those concerned with forest protection have contributed and will contribute a detailed interpretation of the pests concerned. And now let us try give an answer to the third query: »How does the reduction of assimilating apparatus affect the increment?« In order to be able to give an answer to this query, I sorted the samples according to the groups: 0%, 10%, 20%, 30%, 40% etc. where 0 means the samples from Fir trees of the normal assimilating surface, 10% means the trees in which the assimilating surface was reduced by 10%, 20% means the trees in which the assimilating surface was reduced by 20%, etc. On the cores we measured the annual diameter increment during the five-year period of 1966—1970. After the statistical processing of data, we obtained the following results: Loss of needles 10% 20% 30% 40% 50% o% b 326 230 95 33 9 2 d3 50.1 45.8 41.3 45.1 30.8 15.0 cm. 3.82 2.86 2.76 2.38 2.37 1.30 mm. zs (b) = number of samples; (ds) = mean diameter b. h. of Fir trees; (Zs) = average annual diameter increment in the course of the 1966—1970 time interval. |
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If we look at the results obtained, we see that the diameter increment decreases with the reduction of the assimilating surface of the Fir tree. In healthy Fir trees with their crowns intact the average annual diameter increment amounted to 3.82 mm., while it dropped to 2.86 mm. in trees whose assimilating surface was reduced by 10%, and to 2.76 mm. in trees whose assimilating surface was reduced by 20%, etc. It catches our eye immediately that the falling-off diameter increment is not linear, because the reduction of needles by 10% caused a drop of increment by 20%. Regrettably, in groups of 30%, 40% and 50% we have not a large number of samples, because in the investigated forest they were not at our disposal in sufficient amounts. This forest is intensively managed, and thus the trees that lost more than 20% of their needles are rather rapidly removed. Therefore these investigations will be continued in those forests where the dying away of trees spread heavily. Be it as it may, on the basis of performed investigations it is visible that the reduction of assimilating surface by 10% caused a reduction of diameter increment not by the same amount, as one would conclude on first impulse, but by much more. For the purpose of illustration, I mention here the graph in Fig. 6, which I constructed on the basis of these investigations. On the axis of abscissas are plotted the assimilating surfaces of trees, where 1 means the normal assimilating crown, 0.9 means the assimilating crown reduced by 10%, etc., while 0 means the defoliated (de-needled) trees. On the axis of ordinates are plotted the annual diameter increments (Zs) in functional dependence on the assimilating surface expressed in a relative measure. CONCLUSION The dying away of Fir forests had as a consequence the falling-off of increment. In the acidophilous Silver Fir forest community (Abieteto-Blechnetum Horvat) of »Belevine«, Gorski Kotar (Croatia), it was found out by measurements that the diameter increment of Fir has been declining in the 1966—1970 time interval. Maximum reduction of this increment was recorded in 1968 and 1969, after which the increment improved. This decrease of increment is ascribed to the forest pests — defoliators, who attacked the Fir forests in masses. Comparing the diameter increment of healthy Fir trees with that of the infested ones, it was found that on an average the drop of the increment in infested trees was about 30%. The infested trees suffered a definite loss in their amount of needles. Through these investigations we came to the conclusion that the reduction of assimilating surface causes the falling-off of diameter increment, which, for the forest studied, we were able to express by the exponential curve in Fig. 6, where x = 1 means a full crown; x = 0.9 means the crown lacking 10% of its needles; x = 0.8 means the crown which lost 20% of its needles, etc., while 0 means a de-needled tree. From the mentioned curve the following may be seen: — if the assimilating surface is reduced by 10% . . . the diameter increment drops by ca 20% 61 |
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— if the assimilating surface is reduced by 20% . . - the diameter increment drops by ca 35% — if the assimilating surface is reduced by 30% . . . the diameter increment drops by ca 45% — if the assimilating surface is reduced by 40% . . . the diameter increment drops by ca 55% etc. etc. This is the first result of investigations in one forest only. The investigations will also be continued in other forests and under different conditions in order to be able to establish a code. LITERATURA Android , M.: Zaštita šuma na kršu, iz knjige »Simpozij o zaštiti prirode u našem kršu«, str. 93—108, Zagreb 1971. Android , M. i K1 e p a c, D.: Problem sušenja jele u Gorskom kotaru, Lici i Sloveniji, Šumarski list, 1—2, str. 1—13, 1969. god. Chapma n H., Meye r W: Forest mensuration, New York 1949. Klepa c D.: Rast i prirast šumskih vrsta drveća, Zagreb 1953. Klepa c D.: Kako utvrditi postotak smanjenja asimilacijske površine u zaraženim jelovim šumama, Šumarski list, 7—8, 1970. god. O p a 1 i č k i, K.: Mineri i defolijatori jele i njihovo ućešće u procesu sušenja sastojina jele, Šumarski list, 3—4, sir. 69—84, 1970. god. P a r d d, J.: Dendrometrie, Nancy 1961. Prodan , M.: Holzmesslehre, Frankfurt am Main, 1965. S p a i d, I.: Neka ekološka opažanja i rezultati suzbijanja moljca jelinih iglica (Argyresthia fundella F. R.), Šum. list, 5—6, str. 165—189, 1958. god. S p a i d, L: Stanje zaraze i suzbijanje moljca jelinih iglica (Argyresthia fundella F. R.) u 1969. godini, Šumarski list, 11—12, str. 387—397, 1969. god. |